1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, more particularly, a method for manufacturing a semiconductor device so as to provide an efficient manufacturing process while achieving excellent adhesion between electrodes.
2. Description of the Background Art
In recent years, in order to achieve high breakdown voltage, low loss, and the like in semiconductor devices, silicon carbide has begun to be adopted as a material for a semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on-resistance, and the like. Further, the semiconductor device thus adopting silicon carbide as its material has characteristics less deteriorated even under a high temperature environment than those of a semiconductor device adopting silicon as its material, advantageously.
An exemplary semiconductor device adopting silicon carbide as its material is a semiconductor device, such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), for conducting and interrupting a current by controlling appearance/disappearance of an inversion layer in a channel region based on a predetermined threshold voltage. The MOSFET is structured such that an oxide film, electrodes, and the like are formed on a substrate having an active region formed by introduction of a desired impurity or the like. In order to improve reliability of the device, excellent electric contact between the substrate and each electrode as well as high adhesion between the electrodes are required.
In a process of manufacturing such a MOSFET, the substrate having the active region formed therein is grinded, polished, or etched to be thinned to a desired thickness. Thereafter, onto the grinded surface, a contact electrode made of, for example, Ni is formed (for example, see U.S. Pat. No. 7,547,578). The contact electrode reacts with Si constituting the substrate as a result of annealing or the like employing, for example, laser irradiation and is accordingly silicided, thereby making ohmic contact with the substrate. In the case where such a Ni-based electrode is employed as the contact electrode, excellent electric contact can be achieved between the substrate and the electrode. However, when annealing the electrode, deposition of amorphous carbon and formation of irregularities take place on a surface of the electrode. This leads to deteriorated adhesion with a pad electrode to be formed on the contact electrode, with the result that reliability of the device is decreased, disadvantageously (for example, see Zhe Chuan Feng, Jian H. Zhao, “Silicon carbide: materials, processing, and devices”, Volume 20, Taylor & Francis Books, Inc, 2004, pp. 203-280).
Regarding durability of the MOSFET, there is the following problem. That is, due to long-term use, an intermetallic compound having a high resistance may be formed between the contact electrode and the pad electrode to result in a difficulty in stably operating the MOSFET. To address this, for example, study has been conducted with regard to improvement of a metal material constituting the contact electrode and the pad electrode (for example, see Japanese Patent Laying-Open No. 2010-272766).
Further, in the process of manufacturing the MOSFET, heating treatment (sintering) may be performed after the formation of the pad electrode, in order to suppress detachment or the like of the pad electrode due to the deteriorated adhesion between the contact electrode and the pad electrode. Specifically, in the process of manufacturing the semiconductor device such as the MOSFET, the heating treatment is performed after the formation of the pad electrode in order to suppress device yield from being decreased due to the detachment or the like of the pad electrode. This makes it difficult to achieve an efficient manufacturing process, disadvantageously.